An ultrasonic receiver can be used to determine the location of items that contain ultrasonic emitters, such as a mobile device present within a retail, factory, or warehouse environment, for example. The ultrasonic emitter can transmit ultrasonic energy in a short burst which can be received by an ultrasonic transducer (microphone) in the ultrasonic receiver, thereby establishing the presence of the device within the environment.
Further, the use of several ultrasonic receivers distributed within the environment can also be used to provide a specific location of a particular device using techniques known in the art such as triangulation, trilateration, hyperbolic positioning (i.e. multilateration), and the like. Hyperbolic positioning should not be confused with trilateration, which uses distances or absolute measurements of time-of-flight of signals relating to three or more sites, or with triangulation, which uses the measurement of absolute angles. Both of these systems are also commonly used with radio navigation systems, where trilateration is the basis of the global positioning system (GPS). Presently, hyperbolic positioning is required when only time difference of arrival (TDOA) information for signals is available.
The hyperbolic positioning solution is different for different numbers of receiver microphones. Given one TDOA measurement from two microphones (or two receivers), it is a simple calculation to locate the emitter anywhere on one sheet of a two-sheeted hyperboloid. Given two TDOA measurements from three microphones (or three receivers), it is a simple substitution calculation to locate the emitter anywhere on the hyperbola that is the intersection of each of the single sheets of the two, two-sheeted hyperboloids. Given three TDOA measurement from four microphones (or four receivers), the solution leads to three non-linear equations with three unknown values (x,y,z). There are many approaches to solving non-linear equations each with tradeoffs on result certainty, accuracy, run time, and coding complexity. Given four TDOA measurement from five microphones (or five receivers), the solution leads to three homogeneous linear equations which are solvable with tradeoffs on result certainty, accuracy, run time and coding complexity. There are many robust linear algebra methods that can solve for the values of (x,y,z), such as Singular value decomposition or Gaussian Elimination. However, none of the above solutions are able to deliver a result having all of: high accuracy, high confidence, and fast answer determination.
Accordingly, there is a need for an improved technique to resolve the above issues with an ultrasonic locationing system using only TDOA information.
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The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.